3 A hen requires 24-26 hours to produce an egg. Thirty minutes later she starts all over again.If an egg is accidentally dropped on the floor, sprinkle itheavily with salt for easy clean up.Egg yolks are one of the few foods that naturally contain vitamin D.Yolk color depends on the diet of the hen. Natural yellow orangeSubstances such as marigold petals may be added tolight-colored feeds to enhance colors.
5 Composition & Nutritional Value 1. One medium egg contains between 4-5 grams of fat 2. High cholesterol • ~200 mg/egg 3. High in Complete Protein 4. Little to no CHO 5. High in vitamins & minerals • Vitamins A,D,E,K, some B vitamins, selenium, iodine, zinc, iron, copper
7 SHELLThe first line of defence against the entry of bacteria can be brown or white; nutritional value of the egg is the sameComposed mainly of calcium carbonateApproximately 8,000 to 10,000 tiny pores allow moisture and gases in (O2) and out (CO2)SHELL MEMBRANESThere are two membranes on the inside of the shell One membrane sticks to the shell and one surrounds the white (albumen)The second line of defense against bacteriaComposed of thin layers of protein fibres
8 GERMINAL DISCAppears as a slight depression on the surface of the yolkThe entry for the fertilization of the eggWHITE (ALBUMEN)Two layers: thin and thick albumenMostly made of water, high quality protein and some mineralsRepresents 2/3 of the egg's weight (without shell)when a fresh egg is broken, the thick albumen stands up firmly around the yolkCHALAZAA pair of spiral bands that anchor the yolk in the centre of the thick albumen
9 YOLK MEMBRANE (VITELLINE MEMBRANE) surrounds and holds the yolkthe fresher the egg the stronger the membraneYOLKthe egg's major source of vitamins and minerals, including protein and essential fatty acidsrepresents 1/3 of the egg's weight (without shell)yolk colour ranges from light yellow to deep orange, depending on the Xanthophyll content of the ration fed to the hen.AIR CELLforms at the wide end of the egg as it cools after being laidthe fresher the egg the smaller the air cell
10 Characteristics of Fresh/High Quality Eggs • Yolk is high & firm above the white • Small yolk diameter • Yolk is centered in white • High ratio of thick to thin white • High standing thick white
12 Deterioration Changes in Eggs Enlargement of air cell due to loss of moisture spoils the appearance of an egg cooked in the shell.Quality – loss of CO2 ,permits the egg white to become more alkalinePH of egg white may increase from about 7.6 (freshly laid) to in few days.The white becomes thin and spreads when brokenWhite eventually becomes yellow and even cloudy.The yolk flatens.The thinner white is no longer able to keep the yolk in the centre .
13 Egg Candling Larger air cell Yolk off center Speckled appearance Measures quality or freshness without breakingCharacteristics of older, low quality eggs:Larger air cellYolk off centerSpeckled appearance
14 SizesU.S. sizes are defined by the weight of a dozen eggs. (Not individual eggs. An egg in a carton of Extra Large eggs need not weigh at least 27/12 ounces, but the dozen must weigh at least 27 ounces.)Most recipes that call for eggs usually mean Large eggs.SizeWeight of a dozen eggsJumbo30 ouncesExtra Large27 ouncesLarge24 ouncesMedium21 ouncesSmall18 ouncesPeewee15 ounces
15 Preparation of Eggs Dry Heat – Fried – Scrambled – omelets Moist heat – “Boiled” eggs– Coddled eggsprepared in a cup– Poached eggs– A variety ofcustards– Eggs that areprepared using themicrowave
16 Effects of heat on Eggs protein Eggs are useful in binding, thickening and gelling agents because they contain proteins that are denatured by heat leading to :CoagulationGelation
17 Egg whitechanges from a viscous ,transparent sol to an opaque ,elastic solid .Egg yolkincreases in thickness as it is heated becoming either a pasty or mealy solid depending on heatCoagulation TemperatureWhite begins near 60°Cyolk begins near 65°CCoagulation temperature is influenced bypH of the dispersionPresence of saltsHow fast the temperature rises
18 Foam FormationFoams are used as angel food, sponge cakes, meringues,etcWhen the bubbles of air are incorporated in egg white (colloidal dispersion of protein in water) with a wire whip or the blades of a beater, individual proteins contribute aspects of its film –forming potential.The presence of hydrophobic groups with an affinity for air and hydrophilic groups that are soluble in water are essential in lowering surface tension which enable the incorporation of air possible and denaturation of surface protein molecules by heat alter the native conformation and thus stabilize the foam.
19 Volume & Stability Factors Sugar – increases stability – delays foam formation – added at foamy or soft peak stage Acid – doesn’t delay foam formation Fat – decreases foam FormationTemperature– room temperatureUtensils usedsize of the bowl,type of beaterthe finer the wire the thinner the blade, the smaller the cells and the finer the foam.
20 Problems with cooking Eggs Boiled egg if overcooked a green ring is formed around egg yolk due to the presence of iron and sulfur.Can also happen if there is too much iron in cooking water.-chill egg in cold waterCooking leads to the oxidation of cholesterol-increases risk of heart disease
21 Health issues Eggs have cholesterol-increases risk of heart diseases Contamination by salmonella a pathogenic bacteria-hence commercially eggs should be washed with a sanitizing solution after being laidCook eggs to kill pathogenic bacteriaFood allergy esp in infants due to egg albumin hence introduction of egg white to infants is not recommendedRaw egg whites contain a protein called conalbumin that binds iron as well as avidin that binds biotin &can impair function of other B vitamins
23 Milk Milk should contain Milk is ... 8.25% milk-solid-not-fat 3.25% milk fatMilk is ...a true solution for salts, lactose, water-soluble vitaminsmilk is a colloidal dispersion for proteins and some Ca phosphatea dilute emulsion for fat globules
24 Milk pH of milk: 6.6 at 25oC Freezing Point: slightly lower than water when heated, pH decreases, H+ are liberated when Ca phosphate precipitatesFreezing Point: slightly lower than waterLower surface tension than water due to presence of milk fat, protein, free fatty acids, & phospholipids: easy to foamComponents of milk varies with the feed, breed, nutrition & the physiological condition of the cow
25 Nutritional Components of Milk Water: 87%, aw = 0.993Proteins: caseins, whey proteins, enzymesLipids: mainly triglyceridesCarbohydrates: mainly lactose, also glucose, galactose, & other saccharidesSalts (<1%),Vitamins
26 Milk Proteins - Caseins Phosphoproteins, account for 80% of total milk proteinsEasily precipitated by adding acid to pH
27 Milk Proteins - Caseins Acid precipitates caseinsRennin casein: enzyme rennin coagulates caseinsCaseinates: salts of caseins, highly soluble, used as emulsifier, binder, thickening, foaming & gelling
28 Milk Proteins - Whey proteins Not precipitated by acid, but easily denatured by heat (>60C)Four Fractions:lactoglobulins (50%),lactalbumins (25%),serum albuminimmunoglobulinsrich in sulfur-containing amino acids
29 Milk Proteins - Whey proteins Use of whey protein products:Dried Whey: puddings, cakes, baked productsWhey protein concentrates: binder in sausage (up to 3.5%)Ultra Filtered Skim Milk : coffee whitenersCheese Whey: animal feed
30 Milk Proteins - Enzymes Most of the enzymes are inactivated by pasteurizationalkaline phosphatase is an index of adequacy of pasteurization (phosphatase test)Lipase may cause hydrolytic rancidity in dairy products if it is not deactivated
31 Milk Lipids Triglycerides = 98% of total milk lipids Other lipids: phospholipids, free fatty acids, sterols, carotenoids, fat-soluble vitaminsDistinctive dairy flavor due to short-chain saturated fatty acids (C4-C10) : butyric (C4:0), caproic (C6:0), caprylic (C8:0), capric acids (C10:0)Fat content in milk decreases as cow agesFat in feed does not appreciably affect fat content of the milk
32 Milk Carbohydrates Mainly lactose (4.8%), small amount glucose Lactose is the source of lactic acid, formed by bacteria as milk soursAs milk is coagulated, lactose is in the wheyProblems associated with lactoselactose intolerancecrystals from condensed milk or ice creamlumping and caking of dried milk during storage
33 Milk Carbohydrates Use of lactose browning dispersing agent topping & icingcarrier for flavorcolor ingredientsbody & viscosity
34 Vitamins Riboflavin Carotene Milk also provides thiamine & niacin water-soluble, light sensitivelight yellowish & greenish colorCarotenefat-soluble, yellowish color of milkfatskim milk is fortified with retinyl palmitate to replace the carotene in milk fatMilk also provides thiamine & niacinVitamin D is added to almost all milk
35 MineralsRich in Ca and Ptrace elements: Fe, Mg, Mo, Ni, Zn
36 Pasteurization of milk Heating milk at a definite temp for a definite time to destroy pathogens but not all bacteria62oC for 30 min70oC for 15 sec to 100oC for 0.01 sec (HTST)138oC for 2 sec (UHT)to inactivate enzymes (lipase), control rancid & oxidized flavor, and increase shelf life
38 Fermentation of Milk All fermented milk contains lactic acid Undesirable (spoiled products)Desirable (buttermilk, yogurt, cheese)streptococcus lactis initiates the process with lactobacilli spp. continuing the fermentationIncreased thickness due to the association of casein micelles, often accompanied by ß-lactoglobulin.
39 Homogenization of Milk Forces milk through small openings and break up the fat globules.The fat globule membrane is disrupted as new surfaces are createdHomogenized milk is whiter in color, more viscous, more bland in flavor, and foam easily.Less heat stable (curdle more readily), form softer curd
40 Kinds of milkHomogenization – the process of making a stable emulsion of milk fat and milk serum by mechanical treatment and rendering the mixture. Homogenized milk has a creamier structure, bland flavor and a whiter appearance
42 Evaporation & Canning of Milk Evaporated milksterilized canned milk that has been concentrated to about half its original volume by evaporation under a partial vacuum.25% total milk solids including >7.5% milk fathigh temp canning may give cooked flavor (methyl sulfide)storage at high temp for long time may develop off-color (Maillard reaction)
43 Evaporation & Canning of Milk Sweetened condensed milk15% sugar is added after concentration of whole milk through evaporationtotal CHO concentrations of approx. 56% which is sufficient to prevent spoilage by microorganisms
44 Milk FoamsMilk can form gas-in-liquid foams because the milk proteins havelow surface tension - easier to spread the liquid proteins into thin filmslow vapor pressure - reduces the evaporationIn fluid milk, the protein concentration is too low to produce a foam with any stabilityFoams can be formed in evaporated milk or dried milk solids.
45 Effect of Heat on Milk Products ScorchingSome of the whey proteins (-lactoglobulin and -lactalbumin) denature and ppt to form a thin layer of protein on the bottom.This protein gradually undergos the Maillard reaction with lactose, leading to scorching.Scum formationdenatured protein molecules join togetherevaporation of water from the surface (increasing the concentration of casein and salts)
46 Effect of Heat on Milk Products Casien is quite resistant to ppt when heat is applied, but severe heating can cause it to form a curd at pH 7.
48 Composition Meat is the flesh of animals Water content-Appro.75% About 15-20% protein mainly high qualityFat content ranges from 5-30%-varies with the type of animal with the breed, feed and age, pigs convert high % of their feed to fatty tissueMinerals eg Ca in bones, lean muscle rich in Fe and P.Liver excellent source of Fe and Vit.AVitamins-excellent source of niacin and riboflavin. Pork rich in thiamin. meat is deficient in vit.C.
49 Structure of meatCut meat consists of lean tissue which is mainly protein with some bone and fatty tissue.lean meat consists of one or more muscle fibers that is the basic structural unit of meat.Connective tissue provides support for the muscle fibres, fat and bones of meat.Fat is deposited in the connective tissue within the muscle and is known as marbling.
50 Color of meatFresh meat-color differences in color is due to the content of myoglobin concentration in meat (75%) remainder is due to haemoglobin(25%)beef has more myoglobin. Exercised muscles tend to be deeper red eg heel of houndSometimes there is color change in meat-due to change in the pigment myoglobinMolecules of myoglobin contain the iron porphyrin as shown:
51 Resonance of the conjugated double bonds in the porphyrin ring gives rise to the color of meat pigments.
52 Myglobin like haemoglobin can unite temporarily & reversibly with oxygen In live animal, the myoglobin takes O2 from haemoglobin.When the animal dies, O2 supply is cut off. Hence unoxygenated myoglobin in fresh beef is purplish-red in color.Upon exposure to O2,oxymyoglobin is formed which is a bright cherry red colorAt low levels of O2,the myoglobin- O2 complex dissociates ,oxidising the Fe to ferric state resulting in brownish red metamyglobin
53 Cured Meat PigmentsWhen meat eg. bacon, ham, corned beef is cured myoglobin unites with nitric oxide forming nitric oxide myoglobin giving it a light pink colorWhen meat is exposed to low heat during curing, part of the nitric oxide myoglobin is changed to a stable complex (Fe still in ferrous state) The pigment is now called nitric oxide hemochrome.
54 Storing MeatMeat is highly perishable-refrigeration at 4°C or lower reduces the growth of microorganisms on the cut surfaces and maintains freshness.Meat should be frozen if they are not to be used within three daysRaw meats carry pathogens-surfaces they contact should be washed thoroughly to prevent cross contaminationStore :ground meat & variety meat-no longer than 2daysProcessed meats eg slices of ham, frankfurters & lunchen no longer than 5 days in refrigeratorBacon smoked sausage and smoked ham up to 1 week
55 Cooking meatDestroys microorganisms that may have contaminated the surface of meat-should be heated to a temp of 70°C or until juice from meat is clear-not pink in colorAffects tendernessChanges colorAlters water holding capacityDevelops flavor and characteristic aroma
56 Methods of cooking Meat can be cooked by either dry of moist methods Dry methods –meat is cooked added water and uncovered so that the moisture from the meat can evaporate. meat is in contact with hot air, a hot frying pan or hot fat from which heat is conductedMethods include-roasting, broiling, panboiling and fryingRecommended for tender cuts of meat
57 Moist cooking-meat is cooked in a covered utensil, water is added or meat is cooked in the steam/liquid released from the meat as the proteins coagulateBraising (pot roasting &breading) and cooking in water are moist methods of cookingTough cuts of meat are ideal for moist cooking
58 Storage of cooked meatLeftover cooked meat should be cooled promptly and refrigerated at 4°C if they are to be used within 3-4 daysOtherwise they should be frozen at-18°C
59 Effects of cooking on pigments and color When meat is heated the myoglobin is first converted first to oxymyoglobin (bright red color)With further heating, protein moiety of the pigment is denatured, ferrous Fe is oxidized-meat color becomes grayish brown due to denatured globin hemichrome
60 Effect of cooking on meat protein and tenderness Connective tissue-cooking decreases toughness of meat since the tensile strength of meat comes from fibres of collagen that are part of connective tissueMuscle fibres- proteins of muscle fibres are denatured but are not solubilized.They lose their ability to associate with water esp with high temperaturesThis results in shrinkage of fibres and firmness of tissue
61 Flavor-cooking decomposes one or more precursers in the lean meat to give the basic cooked meat tasteLess tender cuts of meat have more extractives-more flavorfulLactones and sulfur containing compounds eg sulfides, mercaptans and cyclic cpds such as pyrazine make important contributions to the flavor of cooked meatsInitial fat content-meat cooked by pan frying and broiling differ little in fat content. Fat melts, causing browning on the surface and increase in flavour.Effect on nutritive value-retention of B vitamins when meat is cooked is good, however there is greater loss of thiamine
62 PoultryIncludes meat obtained from ducks, geese, guineas, pigeons, turkeys and chickens
63 Market class of poultry Different classes of poultry are marketed on the basis of their age that influences tenderness& fat content & dictates the cooking methods.Birds <6 weeks-have no hair on skin and little subcutaneous fat weigh <1kgBroiler-fryer birds-6-8 weeks weigh kgRoasters months-weigh 1-2kgCapon -<8 months-weigh2-4kgHens->1year-weigh 1-2.5kg
64 Preparing poultry for market Birds are killed by cutting the jugular veinDip in hot water(52-54°C loosens feathers without damaging the cuticle of the skinFeathers are removed using machineEvisceration-abdominal cavity is slit &entails removedHead, feet &oil gland are removedBird is chilled-to prevent bacterial growthTenderness of the meat depends on the way meat is cooled-prompt cooling in ice water-meat is tender; slow cooling in air–meat is tough (pH of meat is low 6.3 due to accumulation of lactic acid)
65 Inspection and Grading The following characteristics are considered when grading poultry for quality:Shape and meatinessDistribution of fatGeneral appearance of birdBreaks in skin, bruises and feathers lower the gradeQuality grades for poultry are A,B and C
66 Quality considerations in poultry selection Skin-moist but not sticky, unmarked, light cream in color,slightly blue at the thigh areaFlesh-pink, no bruisingBones-unbroken; flexible breastbone.Pin feathers-noneSmell-freash and cleanTemperature-refrigerated at 0-2°C
67 Common Chicken Cuts Breast Wing Leg Popular way to buy chicken Ideal size for single portionCan be bought with or without skinMeat is usually leanIf skin is removed, the meat can dry out during cookingWingDark meatFairly inexpensive cutQuite fatty contains a large amount of boneIdeal for barbecuingLegDarker meatContains more fat than breastCheaper way to buy chicken but bone in drumstick increases weight so less meat per kilo than breast.Ideal for roasting and frying
68 Handling raw poultryRaw poultry spoils quickly-should be held in the coldest part of the refrigerator and cooked within 2-3 daysFrozen poultry should be thawed in the refrigerator or in changes of cold waterOnce thawed it should be cooked promptlySurface contacted by poultry –wash with warm water and detergent. Cutting boards should be rinsed with sanitizer.this is to prevent cross contamination of other foods-as incidence of Salmonella is high in poultry
69 Composition and structure Comparable to red meat in composition and nutritive valueHas high quality proteinsGood source of B vitamins, Iron and phosphorous. Dark meat is rich in riboflavin. Light meat higher in niacin.Fat content of meat varies-depends on age, feed color of meat. Skin has more fat.The muscles are made of muscle fibres and connective tissue.
70 Cooking poultryCooking method depends on the basis of tenderness. Young poultry can be cooked by broiling, frying, roastingStuffing poultry before roasting-not recommended-stuffing raises temp. slowly –microorganisms (salmonella and staphylococcus) multiply.Microwaving –not recommended as heat is not distributed evenly. Pathogens such as Clostridium perfringens, salmonella and staphylococcus aureus survive microwave cookingMature birds-moist methods allow time to tenderise meat such as stewing and braising.Poultry is cooked when its juice is free of pink color
71 Cooking losses Cooking has little effect on vitamin B retention -90% retention of riboflavin-80% retention of thiaminLeftover cooked poultry-cool promptly and refrigerate at 4°C if it is to be eaten within 2-3 days. Otherwise it should be frozen and held at -18°C
72 Frozen poultry Once thawed-do not refreeze When young chicken are cooked, discoloration in meat next to larger bone may occur- freezing and thawing release haemoglobin from the red cells in the bone marrow as the bones of young chicken is porous and heating denatures the pigment-discolorationDiscoloration is not a problem in older birds-bones are dense.
73 Flavor of cooked poultry Volatile carbonyls such as hydrogen sulfide-give cooked chicken its flavorOtherwise the sulfur compounds present will give only meaty of beef like aroma